Passive RFID (radio frequency identification) devices, based on UHF (ultra-high frequency; 300 MHz-3 GHz) wireless signaling, allow detection and identification of objects in the range of a few meters, and generally have a long shelf life (because these devices do not need to be powered by batteries). UHF systems, however, may not provide accurate localization of objects simply, with location accuracy being on the order of the UHF wavelength (e.g., about 33 cm).